The applicants propose experiments to further investigate the neural mechanisms involved in the neurological effects of low-level microwave irradiation in the rat. In previous research, the applicants found that acute low-level microwave exposure changed the activity of the cholinergic systems in the rat brain, and after repeated exposure, changes occurred in the muscarinic cholinergic receptors. Furthermore, the applicants found that the effects were mediated by endogenous opioids and corticotropin- releasing factor (CRF) in the brain. To further study the neural mechanisms involved, this proposal has the following objectives: 1) to reveal the subtypes of muscarinic cholinergic receptors (M1 and M2) in the brain affected by low-level microwaves; 2) to investigate the subtypes of endogenous opioid receptors (i.e., mu, delta, and kappa) and the loci in the brain where they mediate the microwave-induced changes in cholinergic activity; and to study the possible changes in opioid receptors in the brain after repeated microwave exposure and 3) to determine the location in the brain where CRF mediates the microwave-induced changes in central cholinergic activity. In addition, since the applicant has also found that low-level microwave irradiation affects spatial learning and memory functions, further experiments are proposed to study the neural mechanisms involved in the learning deficient.